The proposed studies serve to investigate differences and similarities in cognitive processes related to hemispheric specialization among primate species including chimpanzees with language-training. This population of chimpanzees offer the unique opportunity to examine whether symbols which have acquired meaning are lateralized in a manner similar to those observed in humans. The objectives of the proposed research are as follows: a) To examine lateralized processing of meaningful and nonmeaningful symbols in human and chimpanzee subjects who use and comprehend visual-graphics symbols with age, sex, species, matched controls. To contrast language-trained chimpanzees patterns of lateralized processing on a variety of tasks with those who have not been reared in a similar environment. b) To assess hemispheric advantages in the processing of facial stimuli and performance on mental rotation tasks in three species"of primate including monkeys, chimpanzees and humans using a visual half-field paradigm designed to test neurologically intact subjects. c) To test hand preference, using multiple measures requiring different manipulation and postural demands, in 100 adult chimpanzees and monkeys. The task are designed so that direct comparative analysis between species can be performed. Moreover, the proposed study will examine cross-sectionally hand preference in chimpanzees and monkeys from different age classes. Finally, heritability of hand preference among related and unrelated chimpanzees and monkeys will be examined. The proposed studies are presented within a neuropsychological framework and will serve to advance our understanding of comparative cognition between species as well as brain-behavior relationships which may accompany different underlying cognitive processes.